Starting to run into this on live sites too, where code was calling has_term() for a previously non-existing taxonomy. Of course that's bad practice, running code like that, but leftover code from long ago started fatal erroring a whole site can be scary for folks with less dev skills to track down what was going on :)

@rpayne7264 Thanks for the suggestion. There has been discussion in the past about this kind of check in wp_list_pluck(), but the general sense is that the PHP notice is a good indicator for developers that they've done something wrong, and should not be silenced. See #35087.